World leaders agreed last year to inject $30bn (£19bn) into forestry and other efforts to tackle climate change between 2010 and 2012. Ahead of bigger, more long-term financing, the "fast-start" money was designed to build trust among poorer countries that produce very miniscule greenhouse gas emissions but suffer many of the worst consequences.

"For most countries, the fast-start money is neither here nor there. It's there in talk, but we don't see it," said Bruno Tseliso Sekoli, the chair of the bloc of least developed countries. "This is very urgent. We need it to adapt to climate change, which is already having an impact on water supplies, land degradation, sea levels and food supplies."

He said his country, Lesotho, has not had any rain since February. "If it stays dry in October, this will go down as the worst drought ever."

Japan has provided $8m (£5m) to improve water supplies and meteorological forecasting, but other countries have been slow to assist. Island states face a similar predicament in the efforts to cope with rising sea levels.

"We need a more aggressive allocation of new, additional funds", said Dessima Williams, chair of the Alliance of Small Island States and Grenada's ambassador to the United Nations.

"We are losing land, losing opportunities, losing income, but we are not demoralised. I have confidence in finding a solution, but I am frustrated that it will not come fast enough."

Wealthy nations have pledged almost all of the $30bn, but climate justice advocates, such as Oxfam, said few of the promises made so far qualify as "new and additional" - the commitment spelled out in the Copenhagen accord.

"The US says it is doubling or tripling climate finance, but there is very little clarity and very little sense that it is new and additional from existing aid flows. A lot of countries are doing this," said Steve Herz of Greenpeace. "They look at what they are doing in other parts of their aid budget, such as on food security, and double count it."

Despite the hold-ups, several negotiators expressed optimism that progress was being made on the longer term finance issue, which should see wealthy nations channelling $100bn (£63bn) per year into climate funds by 2020.

This sum is far short the demands of poorer nations for $600bn (£376bn), or the World Bank's $275bn (£173bn) estimate of the annual cost of tackling climate change by 2030. But the UN secretary-general, Ban Ki-moon, has described the $100bn figure as "significant big money" and established an advisory group to identify where the money can be raised.

Its recommendations, which will be unveiled later this month, will include various mixes of public and private sector financing, according to the coordinator of the advisory group, Daniele Violetti.

This has generated unease among many developing nations and climate activists who are suspicious that the fund will promote speculative carbon markets rather than establish a reliable stream of public funds.

"Financial risk must not be added to the climate crisis," said Susanne Gura of EcoNexus. "It's a question of political will. Developed nations must raise public funds for the south to adapt to climate change and develop while keeping their emissions low."

How to administer the fund is another contentious area. Developing nations would like the money to remain inside the United Nations framework, while others argue it should flow through the World Bank and other institutions. The issue is likely to be fudged this week and at the Cancun conference in November.

Sekoli said the parties would initially just agree to establish a fund and work out the details later. "First we agree on the baby, then teach it to walk or we will be distracted," he said.

China has lent its weight to calls for a solid financial commitment to the developing world, although it says it will not tap into the funds itself.

"Developed nations needs to take historical responsibility and provide finance, but after many years of negotiation they have yet to honour their commitments," said Xie Zhenhua, Chin's chief negotiator.